NOx-decomposing electrode and NOx concentration-measuring apparatus
a technology of concentration measuring apparatus and nox, which is applied in the direction of instruments, material electrochemical variables, manufacturing tools, etc., can solve the problem of not being able to achieve the improvement of the ability to decompose nox
Active Publication Date: 2003-10-30
NGK INSULATORS LTD
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[0012] On the other hand, the ratio of Rh is large in the upper cermet electrode layer as compared with the lower cermet electrode layer. Therefore, the ability to decompose NOx is improved in the upper cermet electrode layer.
[0013] Therefore, in the NOx-decomposing electrode of the present invention, the oxidation reaction and the reduction reaction are suppressed in the measurement of NOx in the lower cermet electrode layer, and the ability to decompose NOx is improved in the measurement of NOx in the upper cermet electrode layer. Accordingly, the NOx-decomposing electrode has high reliability and a long service life.
[0017] Accordingly, it is desirable that the adhesive force is further improved between the ceramic substrate and the NOx-decomposing electrode by changing the ratio between Pt and Rh in each of the cermet electrode layers of the NOx-decomposing electrode and changing the ratio between Pt and Rh between the central portion and the circumferential edge of each of the cermet electrode layers of the NOx-decomposing electrode. That is, about the proportions of Pt in the respective cermet electrode layers of the NOx-decomposing electrode formed directly on the ceramic substrate, the proportion is minimum at a central portion of each of the cermet electrode layers and the proportion is maximum at a circumferential edge of each of the cermet electrode layers.
[0018] Specifically, the ratio of Rh is increased at the central portion of each of the cermet electrode layers of the NOx-decomposing electrode. By doing so, the oxidation reaction and the reduction reaction in the measurement of NOx are suppressed at the circumferential edge of each of the cermet electrode layers, and the expansion and the contraction of each of the cermet electrode layers are suppressed. Therefore, the NOx-decomposing electrode is prevented from exfoliation from the ceramic substrate.
[0019] As described above, the ratio of Rh is large at the central portion of the NOx-decomposing electrode as compared with the circumferential edge of the NOx-decomposing electrode. Therefore, the ability to decompose NOx is improved in the measurement of NOx.
Problems solved by technology
Therefore, it is impossible to realize the improvement of the ability to decompose NOx and the suppression of the oxidation reaction and the reduction reaction in the NOx-decomposing electrode as described above.
Method used
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, F(t) is 0.1% at about 70 cycles. However, in Example 1, F(t) is 0.1% at about 200 cycles. Further, F(t) is 0.1% at about 700 cycles in Example 2, F(t) is 0.1% at about 1200 cycles in Example 3, and F(t) is 0.1% at about 3000 cycles in Example 4. That is, in Examples 1 to 4, the defect ratio F(t) is small and the service life is long as compared with Comparative Example 1.
[0088] With reference to FIG. 3, the proportion of Pt, by which the first cermet electrode layer 62 is occupied, is smallest in Example 1, and it is largest in Example 4. When the results shown in FIGS. 3 and 4 are analyzed, the exfoliation of the detecting electrode 42 from the solid electrolyte layer 12d is hardly caused as the proportion of Pt becomes large in the first cermet electrode layer 62. Therefore, the NOx concentration-measuring apparatus 10 of the embodiment of the present invention has the high reliability and the long service life.
[0089] Next, in the second exemplary experiment, as shown in FIG. 5,...
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Abstract
A detecting electrode comprises a first cermet electrode layer formed directly on a solid electrolyte layer and a second cermet electrode layer formed on the first cermet electrode layer. The ratio between Pt and Rh in the first cermet electrode layer ranges from 100:0 to 25:75 by weight. The ratio between Pt and Rh in the second cermet electrode layer ranges from 25:75 to 0:100 by weight.
Description
[0001] 1. Field of the Invention[0002] The present invention relates to a NOx-decomposing electrode, i.e., an electrode for decomposing or reducing NOx, especially for decomposing NOx to produce oxygen, and to a NOx concentration-measuring apparatus for measuring NOx contained in the atmospheric air or in the exhaust gas discharged from vehicles or automobiles.[0003] 2. Description of the Related Art[0004] NOx contained in an exhaust gas discharged from a vehicle or an automobile is measured. In a conventional measuring method, when an exhaust gas discharged from a vehicle or an automobile is introduced as a measurement gas into a sensor which includes a NOx-decomposing electrode, NOx contained in the measurement gas is measured by measuring an electromotive force generated on the NOx-decomposing electrode (see Japanese Laid-Open Patent Publication No. 11-183434). In this method, the NOx-decomposing electrode is a cermet electrode composed of an alloy of Pt--Rh and a ceramic compone...
Claims
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Login to View More IPC IPC(8): G01N27/419G01N27/407G01N27/416G01N33/00
CPCG01N33/0037G01N27/4074Y02A50/20
Inventor NAKAGAKI, KUNIHIKOSUZUKI, HIDEYUKILEE, SANG JAENAKASONE, OSAMU
Owner NGK INSULATORS LTD